An operational amplifier (op-amp) is used in the comparator circuit shown in the figure below.
Show that the potential at the inverting input of the op-amp is 
.
Explain why the potential difference across resistor R is 
when 
is greater than 
and is zero when is less than .
, so the output voltage of the op-amp is positive (
of 
, so the output voltage of the op-amp is negative (
). Therefore, the diode does not conduct, giving an output voltage 
voltage across resistor R.
